1. Field of the Invention
The present invention relates to the field of mask fabrication for semiconductor processing.
2. Prior Art
Conventional Extreme Ultraviolet Lithography (EUVL) masks are fabricated using metal films to create desired mask patterns. The process of fabricating the mask generally involves forming a metal layer on a substrate, forming a photoresist layer on the metal layer, patterning the photoresist, and etching the metal layer in alignment with the patterned photoresist.
There are several problems associated with metal film masks. For one, it becomes more difficult to transfer accurate images onto a photoresist layer as line widths become smaller. This occurs in part because the etched metal lines on the mask have rough vertical sidewalls. The vertical sidewalls are rough because metal films have relatively large grains. When the metal is etched, the grains protrude from the sidewall. These protrusions become more pronounced as the critical dimension becomes smaller since the grain size remains relatively constant. Current processing methods compound the problem since they cannot control metal line critical dimension variation down to less than 10% of the critical dimension. Consequently, as the critical dimension becomes smaller, grain size will have a greater affect on the image transferred to the photoresist.
There is also a need to repair defects that occur in masks. There are typically two types of defects. The first are clear defects, which form when mask material is inadvertently removed prior to the etch step, causing an unwanted opening in the absorber structure. The second are opaque defects, which form when excess mask material or other debris remain following the etch step, causing intrusions in the pattern openings. Both types of defects must be repaired for an accurate mask image to be transferred onto a photoresist layer.
Thus, what is needed is a method to form a photolithographic mask that will transfer accurate images as critical dimensions become smaller and a method to repair defects in such photolithographic masks.
A method of fabricating a photolithograpic mask is disclosed. First, an etch stop layer is formed over a substrate. Then, a silicon layer is formed over the etch stop layer. Next, a plurality of silicon members and reflective regions are formed from the silicon layer where the reflective regions reflect electromagnetic energy at a predetermined wavelength. Finally, the silicon members are converted into absorption members by forming a nickel silicide that absorbs the predetermined wavelength of electromagnetic energy.